US flu activity nudges up slightly

Mar 23, 2012 (CIDRAP News) – US flu indicators ticked upward this week, with outpatient visits for influenza-like illness (ILI) reaching baseline levels for the first time this season, according to an update today from the Centers for Disease Control and Prevention (CDC).

Four states had high ILI levels and five reported moderate ILI activity, the agency said, while influenza was reported as geographically widespread in 20 states. In addition, the CDC reported three new pediatric flu-related deaths.

The proportion of outpatient visits for ILI reached 2.4% for the week ending Mar 17, which is the US baseline level. Last week it was at 2.2%.

Of 5,088 specimens tested, 1,353 (26.6%) were positive for influenza, up from 23.3% a week ago. Of the positive tests, 1,262 (93.3%) were influenza A and 91 (6.7%) influenza B. H3N2 dominated when subtyping was performed, accounting for 559 (72.6%) of the 770 samples subtyped. The rest were pandemic 2009 H1N1 (pH1N1).

Two Midwestern regions again reported the highest percentage of respiratory specimens testing positive for influenza. Region 5, comprising Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin, jumped from 46.3% last week to 60.7% this week. And percentage in region 7, which includes Iowa, Kansas, Missouri, and Nebraska, rose from 34.0% last week to 39.2% this week.

Twenty states reported regional activity; two reported local activity; and eight states, Guam, and the District of Columbia reported sporadic activity.

Surveillance also turned up another oseltamivir (Tamiflu)–resistant pH1N1 virus, the second one this season, out of 257 pH1N1 viruses tested.

The pediatric deaths were reported during the week that ended Mar 17, but only one occurred that week. The others happened during the weeks ending Feb 4 and Mar 3. They bring the season's total number of pediatric deaths to eight.

In Europe, flu activity continues to abate, the European Centre for Disease Prevention and Control (ECDC) said in an update today. Of 1,203 specimens tested, 41.7% were positive for influenza, down from 43.2% the week before and the third consecutive weekly drop.

Of sentinel specimens tested, 82.9% were influenza A and 17.1% were influenza B. This flu season H3N2 has dominated in Europe, accounting for 97.6% of type A viruses, compared with 2.4% pH1N1.

Sweden is the only European Union country reporting high intensity of ILI. ECDC has yet to find oseltamivir resistance in specimens this flu season.